The final image of the film proper is probably the most beautiful I've seen in any of Polanski's movies. It involves the protagonist facing a castle that is, in fact, the ninth gate a seeker must locate and pass through in order to achieve mystic knowledge and power. We've seen the castle before, in flames; now the sun is setting (rising?) behind it, and it transfigures the castle with a greenish-white light. Then the castle door opens to reveal a blinding whiteness, and Johnny Depp passes inside.
It's a calm image, simple and easily comprehensible despite being a trifle unusual. It works by juxtaposing the solidity of the old stone with the fluidity of light (and by also being the real-world manifestation of a scene we've just been looking at in a 17th-century engraving). It also works because the light is handled so beautifully - the greenish-white is clearly an effect achieved artificially, but that works in its favor, evoking the spillover of heightened reality into reality.
The final image of the film if you include the closing credits is also quite beautiful, but considerably less calm: this is flames dancing against a black background. Because, of course, Our Hero has entered that castle to commune with Old Scratch himself. It may not look like it at the moment, with that haunting greenish-white light emulsing from the doorway to engulf us, but Johnny Depp was going to Hell.
But Polanski saves that implication for the closing credits. Otherwise, this is the closest thing to an undidactic Satan film I've ever seen. That is, it comes on like a horror movie, with baddies on a quest to summon the Devil, but as that quest becomes our hero's, it ceases to feel like such a bad thing - the baddies were bad, but then again they didn't really understand what they were after. Depp does, and he's surely going to gain enlightenment where others failed - after all, the Gatekeeper has chosen him, hasn't she? Like, in a normal devil-worshiper horror film, you'd expect all Hell to break loose (literally), screams and gnashings of teeth and all, to drive home the message that These People Have Delved Too Deep or whatever, that This Is Something That Should Not Be. Not here: here we get an old castle, and a searing, silent, greenish-white light.
But then we do get the flames. I mean, I don't think Polanski's completely disassociating Satan from damnation. But he's toying with it.
And then the flames. It's a little scary.
All told, this isn't a great movie - the natural comparison is to Polanski's earlier Satan movie, Rosemary's Baby, but this isn't that good. It's kind of slow, kind of meandering, and has some scenes that make you wince. But it does have its moments. And that ending'll stick with you.